Catalyst module overheating detection and methods of response

ABSTRACT

According to one aspect, a method of detecting catalyst module overheating in a catalytic combustion system is provided. In one example, the method includes detecting one or more signals from at least one probe adapted to obtain values associated with at least one of the outlet gas temperature of a catalyst module and the outlet face temperature of the catalyst module included in a catalytic combustor. The one or more signals are compared with a preselected value associated with catalyst overheating. The detected temperature may be detected over time to determine a rate of change in the temperature. The temperature may be detected with a UV sensor directed to the catalyst outlet face.

BACKGROUND

1. Field of the Invention

The invention relates generally to catalytic combustion systems andcontrol methods, and more particularly to systems and methods fordetecting and responding to catalyst module overheating or conditionsthat may result in a catalyst module overheating in single ormulti-combustor processes as they relate to and are utilized bycatalytic gas turbine engines.

2. Description of the Related Art

In a conventional gas turbine engine, the engine is controlled bymonitoring the speed of the engine and adding a proper amount of fuel tocontrol the engine speed. Specifically, should the engine speeddecrease, fuel flow is increased causing the engine speed to increase.Similarly, should the engine speed increase, fuel flow is decreasedcausing the engine speed to decrease. In this case, the engine speed isthe control variable or process variable monitored for control. Asimilar engine control strategy is used when the gas turbine isconnected to an AC electrical grid in which the engine speed is heldconstant as a result of the coupling of the generator to the gridfrequency. In such a case, the total fuel flow to the engine may becontrolled to provide a given power output level or to run to maximumpower with such control based on controlling exhaust gas temperature orturbine inlet temperature. Again, as the control variable rises above aset point, the fuel is decreased. Alternatively, as the control variabledrops below the set point, the fuel flow is increased. This controlstrategy is essentially a feedback control strategy with the fuelcontrol valve varied based on the value of a control or process variablecompared to a set point.

In a typical non-catalytic combustion system using a diffusion flameburner or a simple lean premixed burner, the combustor has only one fuelinjector. In such systems, a single valve is typically used to controlthe fuel flow to the engine. In more recent lean premix systems however,there may be two or more fuel flows to different parts of the combustor,with such a system thus having two or more control valves. In suchsystems, closed loop control may be based on controlling the total fuelflow based on the required power output of the gas turbine while fixed(pre-calculated) percentages of fuel flow are diverted to the variousparts of the combustor. The total fuel flow will change over time. Inaddition, the desired fuel split percentages between the various fuelpathways (leading to various parts of the combustor) may either be afunction of certain input variables or they may be based on acalculation algorithm using process inputs such as temperatures,airflow, pressures, and the like. Such control systems offer ease ofcontrol due primarily to the very wide operating ranges of theseconventional combustors and the ability of the turbine to withstandshort spikes of high temperature without damage to various turbinecomponents. Moreover, the fuel/air ratio fed to these combustors mayadvantageously vary over a wide range with the combustor remainingoperational.

A properly operated catalyst combustion system may provide significantlyreduced emission levels, particularly NOx. Unfortunately, however, suchsystems generally have a narrower operating range than conventionaldiffusion flame or lean premix combustors. For example, operation ofcatalytic combustors above desired temperature limits, which may varydepending on the particular application and design of each combustorsystem, may result in thermal damage to the catalytic module. Suchoperation could be a result of a variety of contributing factors insingle or multi-combustor applications, including variations in fuelcomposition outside of specifications, blockage of catalytic channelscaused by foreign objects, lack of uniformity of inlet fuel-air mixture,flameholding in the burn-out-zone radiating heat back to the catalyst,or lack of uniformity of catalytic material on the substrate due tomanufacturing variability. In multi-combustor specific applicationsdiscussed below, operation above desired temperature limits may be aresult of combustor-to-combustor non-uniformities.

The configuration of industrial gas turbines with conventional,non-catalytic combustors, varies from simple single-silo configurations,i.e., one combustor as discussed above, to multiple-combustorconfigurations. The application of industrial, or otherwise, gas turbineengines with catalytic combustion, however, has been limited to thesingle-silo configuration. For example, the Kawasaki Heavy IndustriesM1A-13X and the GE 10 (PGT 10B) gas turbine engines.

The application of catalytic combustion in a multi-combustorconfiguration poses several additional problems that may lead to thermaldamage to one or more catalyst modules. For example, in amulti-combustor configuration there typically are variations fromcombustor-to-combustor due to manufacturing or design differences thatmay lead to variations in pre-burner ignition, catalyst light-off,and/or homogeneous combustion in the burnout zone across the multiplecombustors. Additionally, the combustor sizes are typically reduced toprevent combustor-to-combustor physical interference adding complexityto the design of the combustors. Combustor size reduction can beachieved through flame-holders in the burn-out zone and single-stagecatalyst designs. To supplement the single stage catalyst designs,pre-burners with wide turn-down ratios are generally used. These designchanges will require more complex control of the pre-burner, catalystfuel/air ratio, and/or post catalyst homogenous combustion burnout zoneto ensure the combustion system operates within its operating window.

What is needed therefore is a method and system for detecting catalystmodule overheating or conditions that may result in catalyst moduleoverheating in single and multi-combustor systems. Additionally, methodsof controlling catalytic combustion systems including single andmultiple combustors in response to catalyst module overheating isneeded. Finally, a method and system are needed that reduce thepotential for overshooting and exceeding desired temperature limits forthe catalyst module during transient operations, such as load ramps andthe like.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method of detectingcatalyst module overheating in a catalytic combustion system isprovided. In one example, the method includes detecting one or moresignals from at least one temperature probe adapted to measure at leastone of an outlet gas temperature of the catalyst module and an outletface temperature of the catalyst module included in a catalyticcombustor, or detecting the homogeneous combustion wave locationrelative to the catalyst module. The temperature is compared with avalue associated with catalyst overheating. The homogeneous combustionwave location is compared to a preselected value associated withcatalyst overheating. The detected temperature and/or wave location maybe detected over time to determine a rate of change in the temperatureand/or wave location. The temperature may be detected with athermocouple at the catalyst exit face or an Infrared (IR) thermalsensor directed to the catalyst exit face. The combustion wave locationmay be detected with a UV sensor directed toward the catalyst exit faceand/or the region immediately downstream of the catalyst exit face. Thecombustion wave location may also be detected with metal and/or gastemperature sensors located axially along the burn out zone, or ahydrocarbon or CO sensor located in the flowpath downstream of thecatalyst.

According to another aspect of the present invention, a method forcontrolling a catalytic combustion system is provided. In one example,the method includes detecting a temperature associated with a catalystin a combustor exceeding a preselected temperature, and varying at leastone of fuel flow and air flow to the catalyst and/or preburner to reducethe temperature.

The present invention is better understood upon consideration of thedetailed description below in conjunction with the accompanying drawingsand claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary gas turbine system;

FIG. 2 illustrates an exemplary catalytic combustion system;

FIG. 3 illustrates an exemplary catalytic combustion system withassociated temperature and fuel concentration profiles;

FIGS. 4A-4C illustrate exemplary catalytic combustion systems includingvarious sensors configured for detecting catalyst module overheatingconditions;

FIG. 5 illustrates an exemplary catalytic combustion system with abypass valve and a bleed valve;

FIG. 6 illustrates an exemplary response strategy to catalystoverheating; and

FIG. 7 illustrates an exemplary control method for a load ramp in asingle or multiple combustor system.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides various methods of operating catalyticcombustion systems including detecting, responding to, and preventingcatalyst overheating. The following description is presented to enableany person skilled in the art to make and use the invention.Descriptions of specific structures, functions, techniques, andapplications are provided only as examples. Various modifications to theexamples described herein will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother examples and applications without departing from the spirit andscope of the invention. Thus, the present invention is not intended tobe limited to the examples described and shown, but is to be accordedthe scope consistent with the appended claims.

Exemplary methods and systems are described herein for improved controlstrategies and efficient application of single or multi-combustorcatalytic combustion system or mixed (i.e., catalytic combustion andnon-catalytic combustion) configurations for gas turbine engines.Various methods and systems described herein address issues associatedwith detecting and reacting to actual overheating or potentialoverheating of the catalyst module in a combustor system. Further,methods and systems are described for reducing the potential oftemperature overshoots of the catalyst exit gas temperature in acatalytic combustion system during transient operation of the system,e.g., during load ramp sequences and the like.

Exemplary Catalytic Combustion Systems:

FIG. 1 schematically illustrates an exemplary catalytic combustor gasturbine system including one or more catalytic combustors 1-3 that maybe employed with various methods and systems described herein.Compressor 1-1 ingests ambient air 1-2 through a compressor bellmouth,and compresses the air to a higher pressure driving the compressed air,at least in part, through one or more combustors 1-3 and through thedrive turbine 14. Each combustor 1-3 mixes fuel and air 1-2 and combuststhe mixture to form a hot, high velocity gas stream that flows throughthe turbine 14. The high velocity gas stream provides power to driveturbine 14 and the load 1-5. Load 1-5 may be, for example, a generatoror the like. Although a multi-combustor gas turbine system isillustrated, it should be understood that the present exemplary methodsand systems are applicable to single or multi-combustor gas turbinesystems.

FIG. 2 is a more detailed illustrated of a single combustor 2-6 that maybe included alone or as part of the multiple combustor configuration ofFIG. 1. Catalytic combustor 2-6 generally includes three major elementsthat are arrayed serially in the flow path of at least a portion of theair from the compressor discharge 2-14. Specifically, these threeelements include a fuel injection and mixing system 2-8, a catalyst2-10, and a burnout zone 2-11. Additionally, a preburner 2-20, forexample, a flame preburner (which is positioned upstream of the catalystand which produces a hot gas mixture 2-7) may be included. The hot gasesexiting from the combustion system flow into the drive turbine 2-15 toproduce power that may drive a load. In preferred aspects, there are twoindependently controlled fuel streams, with one stream 2-24 directed toa preburner 2-20 and the other stream 2-25 being directed to thecatalyst fuel injection and mixing system 2-8, as shown. Further, insome examples multiple preburner zones or fuel stages may be employedwith additional independently controlled fuel streams for each fuelstage of preburner 2-20.

In one example, catalytic combustor 2-6 may generally operate in thefollowing manner. The majority of the air from the gas turbinecompressor discharge 2-14 flows through the preburner 2-20 and catalyst2-10. Preburner 2-20 functions to help start up the gas turbine and toadjust the temperature of the air and fuel mixture prior to the catalyst2-10 in region 2-9. For instance, preburner 2-20 heats the air and fuelmixture to a level that will support catalytic combustion of the mainfuel stream 2-25, which is injected and mixed with the flame burnerdischarge gases (by catalyst fuel injection and mixing system 2-25)prior to entering catalyst 2-10. Preburner 2-20 may further be used toadjust the catalyst 2-10 inlet temperature by varying, for example, thefuel or air supply to the preburner 2-20. Ignition of each combustor 2-6in a multicombustor system may be achieved by means of a spark plug orthe like in conjunction with cross fire tubes (not shown) linking thevarious combustors 2-6 as is known in the art. Additionally, a catalyticpreburner receiving inlet air heated electrically or via a smallerstart-up pilot burner may be included.

Partial combustion of the fuel/air mixture occurs in catalyst 2-10, withthe balance of the combustion occurring in the burnout zone 2-11,located downstream of the exit face of catalyst 2-10. Typically, 10%-90%of the fuel is combusted in catalyst 2-10. Preferably, to fit thegeneral requirements of the gas turbine operating cycle includingachieving low emissions, while obtaining good catalyst durability,20%-70% of the fuel is combusted in catalyst 2-10, and most preferablybetween about 30% to about 60% is combusted in catalyst 2-10. In variousaspects, catalyst 2-10 may include either a single stage (as shown) or amultiple stage catalyst including multiple catalysts 2-10 seriallylocated within the combustor 2-6.

Reaction of any remaining fuel not combusted in the catalyst and thereaction of any remaining carbon monoxide to carbon dioxide occurs inburnout zone 2-11, thereby advantageously obtaining higher temperatureswithout subjecting the catalyst to these temperatures and obtaining verylow levels of unburned hydrocarbons and carbon monoxide. Aftercombustion has occurred in burnout zone 2-11, any cooling air orremaining compressor discharge air, e.g., from a bypass valve, may beintroduced into the hot gas stream at 2-15, typically located justupstream of the turbine inlet. In addition, if desired, air canoptionally be introduced through liner wall 2-27 at a location close tothe turbine inlet 2-15 as a means to adjust the temperature profile tothat desired for the turbine section at location 2-15. Such airintroduction to adjust the temperature profile is one of the designparameters for power turbine 2-15. Another reason to introduce airthrough liner 2-27 in the region near the turbine 2-15 would be forturbines with very low inlet temperatures at 2-15. For example, someturbines require turbine inlet temperatures in the range of 900 to 1100°C., temperatures too low to completely combust the remaining unburnedhydrocarbons and carbon monoxide within the residence time of theburnout zone 2-11. In these cases, a significant fraction of the air maybe diverted through the liner 2-27 in the region near turbine 2-15. Thisallows for a higher temperature in region 2-11 for rapid and completecombustion of the remaining fuel and carbon monoxide.

FIG. 3 illustrates an example of a typical existing partial combustioncatalyst system and relative temperatures corresponding to a catalyticcombustor system, e.g., as shown in FIGS. 1 and 2. In such systems, onlya portion of the fuel is combusted within catalyst 3-10 and asignificant portion of the fuel is combusted downstream of catalyst 3-10in a post catalyst homogeneous combustion zone 3-11. Further examples ofpartial combustion catalyst systems and methods of operation aredescribed in co-pending patent application and prior patents, forexample: U.S. patent application Ser. Nos. 10/071,749 and 60/440,940 toD. Yee et al.; U.S. Pat. Nos. 5,183,401, 5,232,357, 5,250,489,5,281,128, 5,326,253, 5,511,972, and 5,518,697 to Dalla Betta et al.;and U.S. Pat. No. 5,425,632 to Tsurumi et al., all of which areincorporated herein by reference in their entirety as if fully put forthherein.

FIG. 3 includes a linear schematic representation of a simplifiedpartial combustion catalytic system illustrated with the gas temperatureand fuel concentrations at various locations along the flow path shownthere below. Air 3-7 enters combustor 3-26 and passes through a fuelinjection and mixing system 3-8 that injects fuel into the flowing airstream. A portion of the fuel is combusted in the catalyst 3-10resulting in an increase in temperature of the gas mixture as it passesthrough catalyst 3-10. As can be seen, the mixture exiting catalyst 3-10is at an elevated temperature. This fuel/air mixture contains remainingunburned fuel that undergoes auto-ignition in the post catalyst burnoutzone 3-11. The burnout zone 3-11 includes the portion of the flow pathdownstream of the catalyst but prior to introduction of additional airand before the turbine where the gas mixture exiting the catalyst mayundergo further reaction. The fuel is combusted in the burnout zone 3-11to form final reaction products including CO₂ and H₂O with thetemperature rising to the final combustion temperature 3-31 athomogeneous combustion wave 3-30 (the region where the remaininguncombusted fuel exiting the catalyst is combusted). The resulting hot,high-energy gases in burnout zone 3-11 may drive the power turbine andload (e.g., 1-4 and 1-5 in FIG. 1).

The lower portion of FIG. 3 illustrates a graph with the gas temperatureindicated on the ordinate and the position along the combustor, or flowpath through the combustor, indicated on the abscissa. The position ofthe graph corresponding generally to the linear combustor diagramdirectly above it. As can be seen, the gas temperature increases as themixture passes through catalyst 3-10 and a portion of the mixturecombusts. Downstream of catalyst 3-10, however, the mixture temperatureis constant for a period, typically referred to as the ignition delaytime 3-32, T_(ignition), before the remaining fuel combusts to form thehomogeneous combustion wave 3-30. The combustion of the mixture in theburnout zone 3-11 thereby further raises the gas temperature.

Homogeneous combustion in the burnout zone is primarily determined bythe ignition delay time of the gas exiting the catalyst. The ignitiondelay time and catalyst exit conditions may be controlled such that theposition of the homogeneous combustion wave can be moved and maintainedat a preferred location within the post catalyst reaction zone. Thelocation of the homogeneous combustion wave 3-30 may therefore be movedby changing, for example, the gas composition (i.e., fuel-to-air ratio),pressure, catalyst outlet temperature, and the adiabatic combustiontemperature (i.e., the temperature of a fuel and air mixture after allof the fuel in the mixture has been combusted with no thermal energylost to the surroundings). For example, by increasing the catalystoutlet temperature T37, the location of the homogeneous combustion wavemoves closer to the catalyst 3-10, and decreasing the catalyst outlettemperature T37 moves the homogeneous combustion process fartherdownstream from the catalyst 3-10. In this way, an exemplary controlsystem may advantageously keep catalyst operation for a single combustoror across multiple combustors within a preferred operating regime forgood catalyst durability while maintaining low emissions. Specifically,when operating in such a preferred operating regime, emissions of NOx,CO, and unburned hydrocarbons may all be reduced while the durability ofthe catalysts may be maintained.

Preferably, the homogeneous combustion wave is located downstream of thecatalyst but not so far downstream that a long reaction zone or volumeis required of the combustor, and not too close to the catalyst modulethat may result in damage to the catalyst module from high temperatures.Ignition delay time depends, at least in part, on the gas composition,gas pressure within the combustor, total mass flow rate/velocity,catalyst outlet gas temperature T37, and adiabatic combustiontemperature. These five parameters may be adjusted in real time by anexemplary control system to change the ignition delay within eachcombustor and compensate for variations from combustor-to-combustoracross the system. For example, various operational methods andstrategies are described in previously cited U.S. patent applicationsSer. No. 10/071,749 and 60/440,940.

In accordance with the present invention, single or multi-combustorcatalytic systems may be controlled to operate with the catalyst modulein predetermined temperature ranges. Further, a multi-combustor systemmay be controlled to achieve uniform position of the homogeneouscombustion wave from combustor-to-combustor as well as operate withsimilar or different temperature ranges across different catalystmodules. The position and temperature may be maintained within preferredranges by operating the system based on a predetermined schedule,wherein a predetermined or calculated schedule is based, at least inpart, on the operating conditions of the catalytic combustor and/or thecatalyst performance. Schedules may be based on operating rangesgenerated from theoretically based models or actual tests of thecombustors in subscale or full scale test systems. For example,predetermined operating schedules for single or multi-combustor systemsare described in previously referenced U.S. patent application Ser. No.10/071,749 and 60/440,940. It should be recognized by those skilled inthe art that various other methods for determining a preferred operatingrange and schedule are possible.

Operation of the catalyst 2-10 above designed temperatures may causematerial damage to the catalyst 2-10, reduced catalytic activity ofcatalyst module 2-10, increased emissions of the system, and the like.Temperatures may increase above desired temperatures for the catalyst2-10 for a large number of factors in a single or multi-combustorapplication including variations in fuel composition outside ofspecification, blockage of catalytic channels in the catalyst 2-10caused by foreign objects, lack of uniformity of inlet fuel-air mixture,flameholding in the burn-out zone 2-11, lack of uniformity of catalyticmaterial on the substrate of catalyst 2-10, and the like. Further, inmulticombustor applications, variations from combustor-to-combustor maycause temperatures to vary above desired ranges for individualcombustors.

Control of the outlet gas temperature T37 of catalyst 2-10 (and thehomogeneous combustion wave location) may be achieved by controlling thepercentages (and, optionally, the total amount) of fuel sent to thepreburner (e.g., fuel line 2-24 and preburner 2-20 of FIG. 2) and/or thecatalyst fuel injection and mixing system (e.g., fuel line 2-25 and fuelinjection system 2-8 of FIG. 2). For example, adding fuel to 2-24 burnsmore fuel in the preburner 2-20 and increases the temperature of the gasmixture at location 2-9, the catalyst inlet. This raises the temperatureat the catalyst outlet temperature T37. Adding fuel at 2-8 changes thefuel-to-air ratio at 2-9 and also increases T37. Further, control of thecatalyst outlet temperature T37 (and the position of the homogeneouscombustion wave 3-30) may be achieved by controlling the airflow of thecombustors with a bypass system, bleed valves, inlet guide vanes, andthe like.

According to one aspect of the present invention, methods and systemsare provided for detecting incidents preceding a potential or actualcatalyst module overheating event, referred to herein as “catalystmodule overheating,” or simply “overheating.” The various aspects areequally applicable to either single or multi-combustor applications.Further, systems and methods are described for responding to andreducing potential or actual catalyst module overheating temperatures.According to another aspect of the invention, control strategies areprovided for reducing the likelihood of temperature overshoots duringtransient operations, such as load ramps and the like for single ormulticombustor systems that may cause catalyst module overheating.

Catalyst Module Overheating Detection:

FIG. 4A illustrates an exemplary linear schematic representation of acombustor 4-26 including various sensors for detecting overheating ofcatalyst 4-10. FIG. 4A illustrates a two stage catalyst including stages4-9 and 4-10. The exemplary system could also be employed with a singlestage catalyst 4-10. In general, regardless of the number of serialstages, inlet thermocouples are disposed at 4-72, outlet thermocouplesat 4-70, and interstage thermocouples (if applicable) at 4-74. As willbe described in greater detail below, upon detection of overheatingtemperatures the system may decrease the temperature of catalyst 4-10.For example, the system may control and alter the catalyst fuel flow tocombustor 4-26 via catalyst fuel valve 4-60 thereby influencing thetemperature of catalyst 4-10. In particular, the fuel flow to thecatalyst 4-10 through fuel valve 4-60 may be controlled, for example, bya feedback measurement of the catalyst inlet or catalyst 4-10temperature thereby influencing the temperature of catalyst 4-10 and theposition of the homogeneous combustion wave 4-30. Further, the airflow4-7 may be varied and managed through bypass valves, bleed valves, inletguide vanes, or the like to vary the temperature of catalyst 4-10.

In one exemplary system, a single ultra-violet (UV) sensor 4-66 islocated in the homogeneous combustion burn-out zone 4-11 as illustratedin FIG. 4A. An exemplary UV sensor includes a Spectra GT10 Flame sensormanufactured by Ametek Power Instruments, but any suitable UV sensor maybe used. UV sensor 4-66 may output a signal proportional to radicalconcentrations within the field of view of UV sensor 4-66, where radicalconcentrations may be used to determine the location of the homogeneouscombustion wave. The field of view of UV sensor 4-66 is directed towardsthe outlet face of catalyst 4-10 to detect the radicals within thehomogeneous combustion wave near the outlet face of catalyst 4-10. Theposition and view of UV sensor 4-66 may vary depending on the particularapplication. Additionally, multiple UV sensors may be used forredundancy or the like.

According to one exemplary method of detecting catalyst moduleoverheating, the output of UV sensor 4-66 may be determined or detectedover time to determine if catalyst 4-10 is overheating or there is apotential for overheating based on the relative location of thehomogenous combustion wave to catalyst 4-10. If the derivative, i.e.,rate of change, of the UV sensor 4-66 output over time is greater than apreselected minimum threshold value for given period of time the systemmay determine a temperature overheating event has or is likely to occur.In this example, the UV sensor 4-66 output is preferably monitored by acontrol system while the engine is operating at a substantially steadystate mode, for example, while operating in speed or Exhaust GasTemperature (EGT) control mode having a substantially uniform turbinespeed of between approximately 95 and 105 percent of fIll speed forsingle shaft gas turbine designs or greater than or equal to idle speedfor two shaft gas turbine designs, and catalyst inlet temperature andcatalyst outlet temperatures are substantially constant. Speed or EGTmodes may include control strategies where fuel and/or air is variedbased on predetermined fuel and/or air schedules associated with enginefundamentals such as the speed, EGT, delta EGT, turbine inlettemperature, compressor discharge pressure, compressor dischargetemperature, and the like. During expected stable conditions, whereengine speed is between approximately 99 and O1 percent for single shaftgas turbine designs but at a stable speed greater than or equal to idlespeed for two shaft gas turbine designs, fluctuations or rapid increasesin temperature may indicate an overheating event. In contrast, duringengine acceleration or loading, the catalyst overheating detectionmethods may be unnecessarily triggered when such conditions, such asrelatively high rates of change in the temperature, are more likely toarise. Therefore, during start up and shutdown, the rate of change of UVsensor 4-66 is not used to monitor overheating or potential overheatingas described above.

The catalyst inlet temperature and catalyst outlet temperatures may bemonitored by temperature probes, such as thermocouples 4-70 and 4-72.Each of the thermocouples represented as 4-70 and 4-72 may be a singlethermocouple or may be a plurality of thermocouples distributed radiallyabout the axis of the combustor. In one example, the temperature isconsidered constant if the temperature does not vary by more than agiven amount, e.g., 10° C., over a given time period. The range and timeperiod will depend on the system and application. Further, the thresholdvalue may be determined or selected based on various factors associatedwith the catalyst module, the combustion system, the control system, andthe like. Various other methods may be used to determine substantiallyconstant catalyst inlet and catalyst outlet temperatures, and in someexamples, may be assiuned constant based on operating modes. Generally,by assuring that catalyst inlet and catalyst outlet temperatures aresubstantially constant, temperature excursions or high values of thecatalyst module temperature or UV-sensor magnitude may be attributed toan overheating event.

According to another exemplary method, catalyst module overheating maybe determined or detected if the magnitude of the UV sensor 4-66 outputis greater than a minimum threshold value. In one example, overheatingis detected if the magnitude exceeds a threshold value for given periodof time. Similarly, the method is preferably performed when the engineis in a substantially steady-state speed, EGT, or similar control mode,and catalyst inlet temperature and catalyst outlet temperatures asmeasured by thermocouples are substantially constant. For example, thesystem is configured to determine that overheating of the catalystmodule 4-10 has or may occur if the UV sensor 4-66 output is greaterthan 12 mA for 5 seconds, while the engine is in a substantiallysteady-state speed, EGT, or similar control mode and the measuredcatalyst inlet gas temperature does not vary by more than 10° C. overthe same time period of 5 seconds, and the average of measured catalystoutlet gas temperature does not vary by more than 5 degrees in thepreceding 40 seconds.

In another exemplary system, which may or may not include UV sensors4-66, various temperature probes, e.g., thermocouples, may be disposedin combuster 4-26 to determine one or more of catalyst inlettemperature, catalyst outlet temperature, or interstage catalysttemperature (if applicable). Catalyst inlet gas temperature may bemeasured by thermocouples 4-72 located immediately upstream of thecatalyst 4-9 inlet face. Thermocouples 4-72 may be disposed a suitabledistance from the inlet face to accurately measure the inlettemperature, e.g., within 4 inches, and preferably within 2 inches ofthe catalyst module 4-9 inlet face. Catalyst interstage gastemperatures, i.e., the gas exiting the upstream stage catalyst 4-9 andentering the downstream stage catalyst 4-10, are measured bythermocouples 4-74 located in the axial space between the upstream anddownstream catalyst stages 4-9, 4-10. Catalyst outlet gas temperaturesare measured by thermocouples 4-70 located a suitable distancedownstream of the catalyst 4-10 outlet face to measure the temperatureaccurately, e.g., within 4 inches and preferably within 2 inches ofcatalyst 4-10. It will be recognized by those skilled in the art thatalternative temperature measurement devices and configurations may beused depending on various design configuration and applications. It willalso be apparent that an exemplary system for performing the followingmethods may include one or more of the UV sensor 4-66, catalyst outletthermocouples 4-70, catalyst inlet thermocouples 4-72, or catalystinterstage thermocouples 4-74. For example, multiple thermocouples maybe arranged in various configurations circumferentially and radiallyaround the inlet and/or exit face of the catalyst modules.

According to one exemplary method, catalyst module overheating may bedetermined or detected if the magnitude of the catalyst outlet facetemperature as measured by a temperature probe, such as an Infrared (IR)thermal sensor 4-67, is greater than a preselected minimum thresholdvalue for a give period of time, while the engine is in substantiallysteady-state speed, EGT, or similar control mode and catalyst inlettemperature remains substantially constant. For example, constantcatalyst inlet temperature may be defined as that which does not vary bymore than 10° C. over a determined time period.

According to one exemplary method, catalyst module overheating may bedetermined or detected if the derivative of one or more of the catalystinterstage temperature thermocouples 4-74, i.e., the rate of temperaturechange of one or more of the thermocouples 4-74, is greater than apreselected minimum threshold value for given period of time, while theengine is in substantially steady-state speed, EGT, or similar controlmode, and catalyst inlet temperature remains substantially constant. Forexample, constant catalyst inlet temperature may be defined as thatwhich does not vary by more than 10° C. over a determined time period.

In case of failure of a thermocouple or other instrumentation such asthermocouple drift or complete failure of a thermocouple to a high orlow state, the system may include fault detection logic to ensure thatinstrumentation failure does not lead to erroneous engine shutdowns. Inone example, where thermocouples are disposed in groups of three or morethermocouples, if any single thermocouple output deviates by more than‘X’ degrees from the combined average, it is determined to be faulty.The value ‘X’ may be based on expected spreads from test results,operational history, or the like. In one instance ‘X’ is between about10° F. and 150° F. In another example, having thermocouples disposed ingroups of two or less, the thermocouple output is compared to a maximumand minimum threshold, based on, e.g., expected temperature ranges fromtest results or operational history. In one instance, ambienttemperature thermocouple outputs are compared to a range of −40° C. and60° C. If any single thermocouple output deviates beyond prescribedmaximum and minimum thresholds, it is determined to be faulty. Themaximum and minimum thresholds for each thermocouple can be based onmanufacturer specifications particular to the thermocouple type. Typicalvalues for N-type thermocouples are −50° F. to 2200° F. If athermocouple is determined to be faulty, it may be no longer considereda valid measurement, and eliminated from further calculations, e.g.,average, maximum, and minimum calculations.

Action taken based on thermocouple failures may differ based on thenumber of ‘good’ thermocouples present in the group (e.g., measuringtemperature at the same station or location), and desired or necessityof redundancy of temperature readings for that particular station orlocation. In one example, if the difference between the total number ofthermocouples in a group and the total number of thermocouples in thatgroup that have failed is less than a given value, an engine shutdownwill be initiated. The value where the engine is shutdown may be basedon criticality of the measured parameter.

It should be recognized by those of ordinary skill in the art that othermethods for determining and accounting for instrumentation failure,e.g., a thermocouple, are possible and contemplated.

According to another exemplary method, catalyst module overheating maybe determined or detected if the magnitude of one or more catalystinterstage thermocouple 4-74 temperatures are greater than a preselectedminimum threshold value for given period of time, while the engine is ina substantially steady-state speed, EGT, or similar control mode, andcatalyst inlet temperature is substantially constant.

According to another exemplary method, catalyst module overheating maybe determined or detected if the spread, e.g., the difference betweenthe highest and lowest, of all catalyst interstage thermocouple 4-74temperatures are greater than a minimum threshold value for given periodof time, while the engine is in a substantially steady-state speed, EGT,or similar control mode, and catalyst inlet temperature is substantiallyconstant.

According to another exemplary method, catalyst module overheating maybe determined or detected if the derivative of one or more catalystoutlet temperature thermocouples 4-70, i.e., rate of temperature change,is greater than a minimum threshold value for given period of time,while the engine is in a substantially steady-state speed, EGT, orsimilar control mode, and catalyst inlet temperature is substantiallyconstant.

According to another exemplary method, catalyst module overheating maybe determined or detected if the magnitude of any one catalyst outlettemperature thermocouple is greater than minimum threshold value forgiven period of time, while the engine is in a substantiallysteady-state speed, EGT, or similar control mode, and catalyst inlettemperature is substantially constant. In this example, exceeding aminimum threshold value for one or more thermocouples may indicate thatfuel is partially and locally igniting resulting in a high temperatureregion at the catalyst inlet which may cause, or potentially cause,catalyst overheating.

According to another exemplary method, catalyst module overheating maybe determined or detected if the spread, e.g., the difference betweenthe highest and lowest of all catalyst outlet temperature thermocouplesis greater than minimum threshold value for given period of time, whilethe engine is in a substantially steady-state speed, EGT, or similarcontrol mode, and catalyst inlet temperature is substantially constant.

According to another exemplary method, catalyst module overheating maybe determined or detected by measuring the preburner (see FIG. 2)temperature rise. The prebumer temperature rise is the differencebetween the preburner outlet temperature and the preburner inlettemperature. If the preburner temperature rise is greater than apreselected threshold value overheating of the catalyst may occur. Forexample, a threshold value may be determined by a schedule of allowablepreburner temperature rises versus preburner fuel flows with the turbinespeed greater than 95% full speed for single shaft gas turbine designsor greater than or equal to idle speed for two shaft gas turbinedesigns, and the turbine in a substantially steady-state speed, EGT, orsimilar control mode. In this example, a preburner temperature rise fora given fuel flow may be higher than expected due to fuel compositionalchanges, and such fuel compositional changes may lead to a catalystoverheating event.

According to another exemplary method, catalyst module overheating maybe determined or detected by a composite model based function oftemperatures and UV sensor output such as y=f(catalyst inlet, catalystinterstage, catalyst outlet, Tad, UV output), where y is compared to athreshold value to determine a potential or actual catalyst overheatingevent. If the model based output y is greater than a predeterminedthreshold value, overheating of the catalyst may occur. It should berecognized by those skilled in the art that various functions havingvarious inputs may be used.

The preburner outlet temperature may be measured downstream of thepreburner and the preburner inlet temperature may be measured upstreamof the preburner by temperature probes such as thermocouples and thelike. Alternatively, the catalyst inlet temperature may, be measured andthe preburner outlet temperature calculated based on the fuel flow rate,fuel temperature, and air flow rate. These methods of detecting thepreburner temperature are illustrative only and other methods ofdetecting the preburner temperature rise are possible.

In the various methods described above, the stable operating conditionsinclude, for example, turbine speed greater than 95% full speed forsingle shaft gas turbine designs or greater than or equal to idle speedfor two shaft gas turbine designs, and operating in a substantiallysteady-state speed, EGT, or similar control mode. In alternative controlsystems, any of the exemplary methods of overheating detection may beused with a reference to similar constant or stable control modes. Theexemplary detection methods are preferably performed during constant orstable control modes to ensure detection of catalyst module overheatingis not triggered when one expects such conditions to arise such asduring engine acceleration or loading, for example, when temperaturemeasurements may rise and fluctuate to a greater extent.

In another aspect of the present invention, different types ofoverheating may be detected. For example, catalyst module overheatingmay be classified under two general categories. The first includes localmodule overheating where a portion or section of the outlet face of thecatalyst module exceeds a desired temperature limit. The second includesglobal module overheating where the entire outlet face of the catalystmodule exceeds a desired temperature limit. Different control methodsdescribed herein may be better suited for particular local or globaloverheating detection. Additionally, various methods may be used aloneor in combination with any other detection method to detect one or bothof local and global catalyst overheating.

Various control strategies were carried out with a Kawasaki HeavyIndustries M1A-13X gas turbine platform including a CESI Xonon™Combustion System to detect both local module overheating and globalmodule overheating of the catalyst 4-10. In one example, the exemplarymethod of measuring the output magnitude of UV sensor 4-66 as discussedabove was carried out to detect local catalyst module overheating. Inparticular, local module overheating was determined if the UV sensor4-66 output exceeded 12 mA for 5 seconds indicating the location of thecombustion wave and the temperature near the catalyst module, while theengine operated in a substantially steady-state speed, EGT, or similarcontrol mode, the catalyst inlet gas temperature did not vary by morethan 10° C. over the same time period, and the average of catalystoutlet gas temperature did not vary by more than 5° C. in the preceding40 seconds. It should be understood, however, that various otherthreshold values, temperatures, and time periods may be varied dependingon the application, control strategy, desired results, and the like.

Further, in examples using the Kawasaki Heavy Industries M1A-13X gasturbine platform, global module overheating was detected by theexemplary method of measuring the catalyst outlet temperature magnitudeagainst a threshold limit. For example, global module overheating wasdetected if the magnitude of the output of any one catalyst outletthermocouple 4-70 exceeded 910° C. for 5 seconds, while the engineoperates in a substantially steady-state speed, EGT, or similar controlmode, and catalyst inlet temperature did not vary by more than 10° C.over 40 seconds. The threshold value of the catalyst outlet thermocouple4-70, in this example of 910° C., may be increased or decreased based onthe age or usage of the catalyst module, e.g., a relatively new or freshcatalyst module where catalytic activity is at its highest may include ahigher threshold value of, e.g., 935° C. Again, it should be understood,however, that various other threshold values, temperatures, and timeperiods may be varied depending on the application, control strategies,desired results, and the like.

It should be recognized that various other configurations of UV sensorsand/or temperature probes may be used to detect catalyst moduleoverheating, including local and global overheating. Further, thevarious methods described herein may be used alone or in combinationwith other control and detection methods.

According to another exemplary method illustrated in FIG. 4B, catalystmodule overheating may be determined or detected by measuring thehomogenous combustion wave front location with respect to the catalyst.FIG. 4B is similar to FIG. 4A, however, a single stage catalyst 4-10design is shown to simplify the description. In this example,thermocouples 4-76 arranged axially and disposed either in the flowpathto measure gas temperatures or metal temperatures on the homogeneouscombustion wave burn-out zone liner (as shown), may provide anindication of location of the homogeneous combustion wave 4-30. Thelocation of the homogeneous combustion wave 4-30 may be determined basedon an increase in temperature as shown in the graph below combustor4-26. As an example, when thermocouples 4-76 at particular location ‘X’with respect to the catalyst 4-10 outlet face detect or measuretemperatures greater than a value ‘Y,’ overheating conditions aredetermined. The thermocouple 4-76 location ‘X’ may be based on a safedistance necessary for control system response, and the temperaturevalue ‘Y’ based on Tad. In one example, the thermocouple location ‘X’ is12 inches from the catalyst outlet face, and the temperature value ‘Y’is 10001C. Although a plurality of thermocouples 4-76 are illustrated, asingle thermocouple 4-76 could be used.

According to another exemplary method illustrated in FIG. 4C, catalystmodule overheating may be determined or detected by measuring thehomogenous combustion wave 4-30 location with respect to the catalyst4-10 with at least one gas emissions analyzer port 4-78. When emissionsanalyzer port(s) 4-78 at location ‘X’ indicate hydrocarbon and/or COcontent less than ‘Z’ ppm, overheating conditions are detected. Thegraph shown below combustor 4-26 illustrates generally the levels ofhydrocarbon (HC) and CO concentrations relative to the homogeneouscombustion wave location 4-30. The value ‘X’ is similar to thatdiscussed with regard to FIG. 4B, and the value ‘Z’ may be based onhydrocarbon and/or CO content after almost complete combustion. In oneexample, ‘X’ is 12 inches, and ‘Z’ is 50 ppm. Additionally, because theexemplary catalyst overheating detection methods are generally used forsubstantially steady state conditions, time delay associated with thesampling may be permissible.

Catalyst Module Overheating Response Strategies:

According to another aspect of the present invention, methods forresponding to possible or actual catalyst module overheating conditionsare provided. Generally, the exemplary methods and strategies can becategorized as methods predominantly resulting in a reduction incatalyst inlet fuel-air ratio, and strategies predominantly resulting ina reduction in catalyst inlet temperature.

The air management system of the combustor system, including, forexample, bypass, bleed, and/or compressor inlet guide vanes as describedbelow, may be utilized to increase catalyst air flow and thereby reducethe catalyst inlet fuel-to-air ratio. Reducing the catalyst inletfuel-to-air ratio may reduce the temperature of the catalyst module andprevent or reduce catalyst over heating. Reducing catalyst fuel flow mayalso reduce the fuel-to-air ratio. Additionally, reducing the preburneroutlet temperature and/or reducing catalyst fuel temperature may reducecatalyst inlet temperature. Other suitable methods for varying thefuel-to-air ratio or catalyst inlet temperature may be used. Specificstrategies employed may be specific to the system and its operatingcycle conditions.

An exemplary bypass system that may be controlled to vary the catalystair flow and fuel-to-air ratio is illustrated in FIG. 5. The bypasssystem 5-39 extracts air from a region 5-21 near the inlet of preburner5-20 and injects the air in a region 5-13 downstream of the postcatalyst reaction zone 5-11 but upstream of the power turbine inlet5-15. Bypass air can also be extracted at the outlet of the compressor,at any location between the compressor outlet and the preburner 5-21, ordownstream of the preburner 5-20 and before the inlet to the catalyst5-10. Flow meter 5-41 may measure the bypass airflow and valve 5-40 maycontrol the bypass airflow. The bypass flow from region 5-21 to region5-13 is driven by the pressure difference with region 5-13 at a lowerpressure than region 5-21. This pressure difference is due to thepressure drop that occurs through the combustor including the preburner5-20, the catalyst fuel injection and mixing system 5-8, and thecatalyst 5-10. The bypass system 5-39 allows for the control of the airflow entering the catalyst by controlling the combustor airflow. Thebypass system 5-39 may thereby influence the temperature of the catalystmodule as well as control the homogeneous combustion wave in the burnoutzone 5-11 of combustor 5-26.

FIG. 5 also illustrates an exemplary bleed system that may be used aloneor in combination with bypass system 5-39 for controlling the airflow ofcombustor 5-26. The bleed system extracts air from a region near thecompressor discharge 5-14 and vents it to the atmosphere. A flow meter5-43 may measure the flow of bleed air and valve 5-42 may control flowof bleed air. The bleed flow from 5-14 to atmosphere is driven by apressure difference with 5-14 being higher pressure than atmosphericpressure.

Exemplary combustors may also include inlet guide vanes (not shown) tovary the amount of airflow through the engine and combustor. Inlet guidevanes generally include a set of vanes disposed at the inlet of thecompressor that may be selectively rotated to vary the airflow into thecompressor and therefore the total airflow through the system. The inletguide vanes may be used to reduce (or increase) airflow and increase (ordecrease) the fuel-to-air ratio within the combustor to stay within adesired operating range.

One exemplary method for responding to actual or potential catalystmodule overheating includes closing the bypass valve 5-40, which isgenerally at least partially open during operation. Closure of thebypass valve 5-40 is induced by a reduction in adiabatic combustiontemperature demand (Tad) and results in a decrease in the catalyst inletfuel-to-air ratio. It will be understood by those of ordinary skill inthe art that alternate methods of closing the bypass valves may beimplemented and would depend on how the process variable used for thebypass valve control is related. The bypass valve 5-40 may be closedpartially, followed by a waiting period to determine if the reductionhas reduced or eliminated the catalyst 5-10 overheating. For example,the output from a dEGT versus Tad demand value may be temporarilyreduced by a predetermined percentage ranging from 0.1 to 10%. DEGT maybe used to specify operation at a preferred point on an operating lineof the system. DEGT at time t is defined as the calculated exhaust gastemperature at full load at time t (EGT_(full load-t)) minus the exhaustgas temperature value at time t (EGT_(t)) and expressed as follows:dEGT=EGT _(full load-t,) −EGT _(t)

The exhaust gas temperature at full load (EGT_(full load-t)) may becalculated from current operating parameters such as ambient temperatureand ambient pressure at any time t and represents the expected exhaustgas temperature when the turbine is running at full load (100% load).The current exhaust gas temperature (EGT_(t)) is the measured value ofthe exhaust gas temperature at any time t. Subtraction of these valuesgives the DEGT at time t.

If the overheating has subsided after reducing the DEGT versus Taddemand value bypass valve 5-40 may return to its previous operatingsetting or range. If the overheating has not subsided, the bypass valve5-40 may be closed further followed by further monitoring. Incrementalreductions in Tad demand may be made until the bypass valve 5-40 isfully closed or the overheating has subsided.

Referring to Table A below, there are, for example, three schedules ofdEGT versus Tad demand and demand temperature at location 5-7, referredto herein as T34 (see also FIG. 2), for three different levels ofcatalyst activity (1, 2 or 3). TABLE A Operating Schedules dEGT vs. Tadand T34 schedules Tad T34 Tad T34 Tad T34 % dEGT Demand 1 Demand 1Demand 2 Demand 2 Demand 3 Demand 3 Load (° C.) (° C.) (° C.) (° C.) (°C.) (° C.) (° C.) 100  0 1300 500 1310 505 1320 510 90 35 1275 505 1285510 1295 515 80 70 1250 510 1260 515 1270 520 70 105 1225 520 1235 5251245 530 60 140 1200 530 1210 535 1220 540 50 175 1175 555 1185 560 1195565 40 210 1150 580 1160 585 1170 590 30 245 1125 605 1135 610 1145 61520 280 1100 650 1110 650 1120 650 10 315 1075 650 1085 650 1095 650 FSNL350 1050 650 1060 650 1070 650

Another exemplary method for responding to catalyst module overheatingincludes varying the air flow through the system with a bleed valve5-42. The methods may be carried out similar to the bypass valve 5-40methods described above.

Another exemplary method for responding to catalyst module overheatingincludes decreasing the catalyst inlet temperature by reducing thepreburner fuel flow. With reference again to FIG. 2, reduction inpreburner fuel flow 2-24, which may be induced by a reduction inpreburner outlet gas temperature demand, results in a decrease inpreburner outlet temperature, referred to herein as “T34,” and catalystinlet temperature, referred to herein as

Another exemplary method for responding to catalyst module overheatingincludes reducing catalyst fuel flow. Reduction of catalyst fuel flow2-25, which may be induced by a reduction in engine load demand, resultsin a decrease in catalyst inlet fuel-to-air ratio and catalyst outlettemperature T37. Reductions of catalyst fuel flow 2-25 may be madeincrementally, followed by periods of monitoring, as described above. Itshould be recognized, that there are numerous methods for reducing fuelflow, e.g., acting on a fuel valve directly, varying a signalcontrolling fuel flow, and the like.

Additional control strategies can be developed to achieve similarresults. Those of ordinary skill in the art of controls, control systemsand/or catalytic combustion control algorithms can develop alternativeand equivalent approaches to bypass valve closure, reduction inpreburner fuel flow, and decrease in catalyst inlet fuel flow to resultin lower catalyst inlet temperatures and fuel-to-air ratios based ontheir knowledge and the disclosure herein.

The exemplary methods may be performed alone or in any combination. Inone example, illustrated in FIG. 6, several exemplary methods describedabove are performed in a predetermined series until the catalystoverheating, or potential of overheating, is reduced. In a firstresponse approach, upon detection of potential or actual catalystoverheating conditions in block 6-1, the control system may respond byreducing the bypass air flow in block 6-2. This is incorporated bytaking the output from a DEGT versus Tad demand value and temporarilyreducing the demand value by a predetermined percentage that may rangefrom 0.1 to 10%, and preferably 1 to 2%. For example, if thepredetermined percentage is 1.5% and the Tad demand value is 1340° C.,the temporarily reduced value is1340−(1340*1.5%)=1319.9° C.

If the first reduction in Tad demand eliminates the detectedoverheating, then this temporary reduction may be held for apredetermined fixed duration, e.g., 55 seconds, after which the Taddemand returns to its original set-point. However, if the firstreduction is not successful in eliminating the detected overheating, Taddemand is reduced by an additional percentage, 1.5% in this example;however, the percentage may vary for each incremental decrease. Thisseries of incremental percentage reductions continue until the Tadcannot be reduced further because the bypass is fully closed, afterwhich a second response approach may be activated.

In a second response approach to the catalyst module overheatingconditions, the control system may respond by reducing the preburnerfuel flow in block 6-3. This is incorporated by taking the output from aDEGT versus T34 demand value and temporarily reducing it by apredetermined percentage that ranges from 0.1 to 10%, and preferablybetween 1 and 2%. For example, if the predetermined percentage was 1.5%and the T34 demand value is 510° C., the temporarily reduced value is:510−(510*1.5%)=502.4° C.

If the first reduction in T34 demand eliminates the detectedoverheating, then this temporary reduction is held for a predeterminedfixed duration, e.g., 55 seconds, after which the T34 and Tad demandsreturn to their original set-points. However, if the first reduction isnot successful in eliminating the detected overheating, T34 demand maybe reduced again, e.g., by another 1.5%. This may continue until thepreburner fuel flow is at its minimum level to sustain flame, afterwhich a third response approach may be activated if needed.

In a third response approach to the catalyst module overheatingconditions, the control system may respond by reducing the engine fuelflow demand in block 6-4. This is incorporated by taking the GeneratorLoad set point, e.g., the desired output of a power plant or the like,and ramping it down 25 kW (e.g., past the point where the Generator Loadset point crosses over the Generator Load feedback). If the firstreduction in Generator Load set-point eliminates the overheat detection,then this temporary reduction is held for a predetermined fixedduration, e.g., 55 seconds, after which the Generator Load, T34, and Tadreturn to their original set-points. However, if the first reduction isnot successful in eliminating the overheating conditions, Generator Loadset-point is reduced by an additional 25 kW. This series of reductionsand pauses may continue until load is dropped to a level, e.g., below anemission guarantee range, upon which time the engine may automaticallyunload and shut-down.

During application of the above strategies it was noted that the release(when set-points return to normal) of the first, second, and thirdapproaches sometimes resulted in an overshoot in fuel-to-air ratio,which in itself triggered additional catalyst module overheating events.To compensate for this occurrence an additional strategy may beincorporated. For every three overheating responses, the operatingschedule may be decreased by one (see Table A, e.g., reducing fromschedule 3 to 2, or from schedule 2 to 1). Although this caused thecatalytic combustion system to operate temporarily under coolerconditions, steady-state catalyst exit gas temperature feedback basedadaptive control logic may increase the operating schedule back to itsoriginal value over time. Such exemplary control methods and systems forcatalytic combustion systems, including a bypass valve and/or bleedvalve system, are described in U.S. patent application Ser. No.10/071,749 and 60/440,940, which are incorporated herein by reference intheir entirety.

It should be understood that the exemplary method of FIG. 6 is exemplaryonly and the various responses in blocks 6-2 through 6-4 may be carriedout in any order as well as in parallel. Also, additional methods toreduce catalyst module overheating, e.g., including a bleed valve orinlet guide vanes to vary airflow and air-to-fuel ratios, may also beincluded and carried out in series or parallel.

Control Strategies During Transient Operations:

According to another aspect of the present invention, methods andsystems are provided for reducing or eliminating overshoots in thecatalyst outlet gas temperature T37 beyond desired thresholdtemperatures. Overshoots in the catalyst outlet gas temperature maycause damage to the catalyst module or combustion system. Catalystoutlet gas temperature overshoots occur primarily during transient modesof the system, such as during load ramps, engine accelerations,startups, and the like. Temperature overshoots are generally caused byovershoots in the fuel-to-air ratio resulting from either overshoots inthe fuel and/or lagging response of the air management system, e.g.,including a bypass valve control system, a bleed valve control system,and an inlet guide vane control system. It should be recognized thatother factors may contribute to or cause temperature overshoots directlyor indirectly and may be reduced by exemplary methods described herein.

Generally, a catalytic combustion system includes a predeterminedtemperature or trip limit relating to the catalyst outlet gastemperature T37 to prevent damage to the combustor and turbinecomponents due to undesirably high temperatures. Transient overshootsmay put the T37 temperature values above the trip limit, resulting inengine shutdowns to reduce the potential for damage. Therefore, reducingthe potential for temperature overshoots reduces the potential fortemperature related damage to the catalyst module and combustion systemas well as reducing unanticipated engine shutdowns.

In one example, reducing the effective load ramp rate may reducetransient overshoots. This would impact the rate at which the dEGT ischanged to meet the desired generator load setpoint is achieved. Theeffective load ramp rate may be reduced using two methods and may beused alone or in combination: (a) uniform reduction in load ramp ratedemand, or (b) incremental load ramp steps followed by pauses (whenintermediate generator load setpoint is held constant), until the finalgenerator load setpoint is achieved. Depending on the particular systemand application, load ranges, ramp rates, and pause times may be chosento reduce the potential for overshoots of the catalyst outlet gastemperature. Other engine fundamental quantities associated with engineload such as EGT, ambient temperature, compressor discharge pressure,compressor discharge temperature, and the like may be substituted forDEGT.

In another example, transient overshoots may be reduced by the reductionof T37 prior to the execution of load ramp operations (pre-ramp T37).For example, a reduction in fuel or an increase in air through thecatalyst module prior to a load ramp operation may decrease thepotential for an overshoot of T37 during or subsequent to the load ramp.Generally, air is increased while fuel remains constant to maintaingenerator output. In one example, both fuel and air are reduced but fuelis reduced more than air such that the net fuel air ratio in thecatalyst is decreased.

Alternatively, catalyst inlet temperature T36 may be reduced by areduction in T34 demand, which may decrease the potential for anovershoot of T37 during or subsequent to the load ramp.

In another example, transient overshoots may be reduced through T37limit feedback control, where the effective load ramp rate is limited atleast partially on pre-established T37 upper and lower limits of thesystem. When T37 reaches the upper limit during a load ramp, the loadramp pauses until T37 drops below the lower limit, at which time theramp continues to increase until the final load set-point or upper loadlimit is reached.

The exemplary methods described above may be employed alone or in anycombination to reduce the potential for overshoots in T37. In oneexample, reducing T37 prior to execution of load ramps may be used inconjunction with reducing the load rate. The combination of both methodsmay be more effective than either method alone. Other similar andequivalent strategies apparent to those of ordinary skill in the art andmay be used with the exemplary methods described.

FIG. 7 illustrates an exemplary control strategy for reducing thepotential for overshoots in the catalyst outlet gas temperature duringtransient operations such as load ramps and the like. An exemplarycontrol strategy was implemented on a Kawasaki Heavy Industries (KHI)M1A-13X gas turbine engine equipped with a CESI Xonon™ CombustionSystem. As will be recognized by those of skill in the art, othersimilar or non-similar gas turbine systems may also be used with theexemplary control strategies.

In block 7-1, the system is initially controlled at a ramp rate X untilDEGT reaches 200° C., where ramp rate X represents the default ramp ratefor the particular application. In one example the ramp rate was set to25 kW/sec. The DEGT threshold value may be preselected and based atleast in part on test results. In one example, several tests wereconducted to determine a load range in which the transient T37 peaksexceeded set limits for the particular system. Testing revealed that theT37 overshoots were most intense and had the highest propensity toexceed preset limits in the range of 70% to 100% of the full load. Inthis example, dEGT=200 corresponds to approximately 70% load such thatthe engine is ramped to the lower end of the range where overshoots arelikely to occur for the particular system at the default ramp rate. Itshould be recognized that various other engine fundamental quantitiessimilar to engine load can be substituted for DEGT. Further, the valueof DEGT may vary depending on the particular application and system.

The exemplary method may include a tunable pause in block 7-2 to allowthe system to respond to the ramp rate. In this particular example thetunable pause was set at 0 seconds because the system response wasadequate without such a pause. In alternative applications and systems,however, a tunable pause may be useful and desired.

In block 7-3, the control strategy determines if the catalyst exittemperature T37 is less than a predetermined threshold temperature. Inthis example an average temperature T37 is measured where thetemperature is the instantaneous average of all T37 thermocoupleoutputs. In this example, the threshold temperature was selected at 870°C. The threshold value may be chosen, at least on part, on minimizingthe T37 overshoots during ramps, and minimizing delay time caused byoperating in the loop from block 7-3 to block 7-6 and back to block 7-3(as shown in FIG. 7 and described below). Further, the threshold valuemay vary depending on the particular system and application and may begreater for a catalyst module in its initial use when catalyst activityis generally at its highest. In this example, testing showed that thethreshold value may be increased to approximately 880° C. for a catalystmodule during its first 500 hours of operation. The comparison of T37average to the threshold value results in the control strategy flowingeither to block 7-7 if the average temperature of T37 is less than apredetermined threshold, or to block 7-4 if the average temperature ofT37 is greater than the predetermined threshold.

In block 7-4, another tunable pause may be performed to allow the systemto respond. In this example, the tunable pause was again set at 0seconds; however, in other applications and system configurations atunable pause of varying lengths may be useful and desired.

In block 7-5, the operating schedule is dropped per a look-up table,e.g., Table B shown below, where Table A above includes exemplaryoperating schedules. Schedule decrements may be used as a method toreduce pre-ramp T37. In an effort to minimize delay time caused byoperating in the loop from block 7-3 to block 7-6 and back to block 7-3(as shown in FIG. 7), a look-up table that will drop schedules based onthe deviation of T37 average from the set-point in block 7-3 may beused. An example of this look-up table is shown in Table B. TABLE BSchedule Decrement Look-up Table: Number of T37 Avg schedulesInstantaneous to Range (° C.) decrement 860-870 1 870-880 2 880-8903 >890 3

In block 7-6 an additional tunable pause may take place to allow thesystem to respond to the schedule decrement. In this example, a tunablepause of 10 seconds is performed. The tunable pause may allow thecombustion system to respond to the schedule drop in block 7-5, and toregister a drop in T37 average. The length of tunable pause in block 7-6may vary depending on the particular system and application.

Returning to block 7-3, if T37 is less than the predetermined threshold,e.g., 870° C., the system ramps to the final set-point at a rate equalto X-Y in block 7-7, where Y may be set between 0 and the value of X toreduce the ramp rate. In this example, X=25 kW/sec, and Y=0 kW/sec.Increasing Y above 0 allows incorporation of a reduced ramp rate ifdesired. Both X and Y will vary depending on the particular system andapplication.

In block 7-8 schedules may be incremented up, for example, to theoriginal schedule, i.e., the original schedule number prior to rampingload in block 7-3. Schedules may be incremented, e.g., one at a time,with a delay of 5 seconds after each increment, and a comparison with aT37 threshold=865° C. before performing each increment. This T37threshold was chosen based on minimizing CO emissions of the particularsystem, however, other increments, delay times, and thresholds, arecontemplated. The original schedule (in block 7-3) may be chosen basedat least in part on minimizing the time spent at a schedule lower thanthe original schedule in order to minimize CO emissions, and minimizingthe time before the controls logic can allow load to be ramped again.

In block 7-9 the control strategy may ramp again if desired. In oneexample, the control logic may allow load to ramp again only if T37exceeds a minimum set-point. In the present example, the minimumset-point is 865° C.

When steady state operation is reached in block 7-10, the schedules maybe incremented or decremented based on T37 feedback. For example,adaptive control logic may use T37 average feedback to incrementschedules as desired during steady state operation. It should beunderstood that the method of FIG. 7 is exemplary only. Additionalmethods to reduce potential overshoots may also be included and carriedout in series or parallel.

Exemplary control methods and systems for carrying out the variouscontrol methods are described in U.S. patent application Ser. No.10/071,749 and 60/440,940, which are incorporated herein by reference intheir entirety. Further, it should be understood that the abovedescribed methods and control systems throughout this detaileddescription may be performed by hardware, software, firmware, orcombinations thereof.

The above detailed description is provided to illustrate exemplaryembodiments and is not intended to be limiting. It will be apparent tothose skilled in the art that numerous modification and variationswithin the scope of the present invention are possible. Accordingly, thepresent invention is defined by the appended claims and should not belimited by the description herein.

1. A method for detecting catalyst module overheating in a catalyticcombustion system comprising the acts of: detecting one or more signalsfrom at least one probe adapted to obtain values associated with atleast one of an outlet gas temperature of a catalyst and an outlet facetemperature of the catalyst included in a catalytic combustor; andcomparing the one or more signals with a value associated with catalystoverheating.
 2. The method of claim 1, wherein detecting the one or moresignals includes detecting at least one of an average temperature andmaximum temperature.
 3. The method of claim 1, wherein the one or moresignals are detected over a period of time.
 4. The method of claim 1,wherein detecting the one or more signals includes detecting a rate ofchange in the temperature.
 5. The method of claim 1, wherein detectingthe one or more signals includes determining at least one of an averagetemperature and maximum temperature associated with multiple temperatureprobes.
 6. The method of claim 1, wherein the one or more signals aredetected during a turbine speed approximately 95% or greater of fullspeed for a single shaft gas turbine.
 7. The method of claim 1, whereinthe one or more signals are detected during a turbine speed greater thanor equal to idle speed for a two shaft gas turbine.
 8. The method ofclaim 1, further including determining an inlet temperature of thecatalyst, wherein the catalyst inlet temperature is substantiallyconstant when determining the temperature associated with at least oneof the outlet gas temperature of the catalyst and the outlet facetemperature of the catalyst.
 9. The method of claim 1, wherein the oneor more signals are detected during a substantially stable control mode.10. The method of claim 1, wherein detecting the one or more signalsincludes infrared thermal sensor with a field of view directed to anoutlet face of the catalyst.
 11. The method of claim 1, whereindetecting the one or more signals includes one or more temperatureprobes located downstream of the catalyst.
 12. The method of claim 1,wherein detecting the one or more signals includes one or moretemperature probes located upstream of the catalyst.
 13. The method ofclaim 1, further including determining an interstage gas temperaturebetween the catalyst and a second catalyst located serially in thecatalytic combustor.
 14. The method of claim 1, further including atleast a second catalytic combustor arranged in a multi-combustorconfiguration.
 15. A method for detecting catalyst module overheating ina catalytic combustion system comprising the acts of: determining theposition of a homogenous combustion wave relative to a catalyst includedin a catalytic combustor; and comparing the position with a valueassociated with the catalyst overheating.
 16. The method of claim 15,wherein the position of the homogenous combustion wave is determined byan ultraviolet sensor.
 17. The method of claim 16, wherein detecting theposition of the homogenous combustion wave includes determining amagnitude of the ultraviolet sensor.
 18. The method of claim 15, whereinthe position of the homogenous combustion wave is measured over time.19. The method of claim 15, wherein detecting the position of thehomogenous combustion wave includes determining a rate of change in thehomogeneous combustion wave position.
 20. The method of claim 15,wherein determining the position of the homogenous combustion waveincludes determining an average position associated with multipleultraviolet sensors.
 21. The method of claim 15, wherein the position ofthe homogenous combustion wave is determining during a turbine speedapproximately 95% or greater of the full speed for a single shaft gasturbine.
 22. The method of claim 15, wherein the position of thehomogenous combustion wave is determined during a turbine speed greaterthan or equal to idle speed for a two shaft gas turbine.
 23. The methodof claim 15, further including detecting an inlet temperature of thecatalyst, wherein the catalyst inlet temperature is substantiallyconstant when determining the position of the homogenous combustionwave.
 24. The method of claim 15, wherein the position of the homogenouscombustion wave is determined during a substantially stable controlmode.
 25. A method for detecting catalyst module overheating in acatalytic combustion system comprising the acts of: detecting a firsttemperature associated with a preburner inlet temperature, detecting asecond temperature associated with a preburner outlet temperature;determining a difference between the second temperature and the firsttemperature; and comparing the difference with a value, wherein thevalue is associated with a catalyst located downstream of the preburneroverheating.
 26. The method of claim 25, wherein the value is associatedwith the catalyst overheating.
 27. The method of claim 25, wherein thetemperature is detected during a turbine speed approximately 95% orgreater of full speed for a single shaft gas turbine.
 28. The method ofclaim 25, wherein the temperature is detected during a turbine speedgreater than or equal to idle speed for a two shaft gas turbine.
 29. Themethod of claim 25, wherein the temperature is detected during asubstantially stable control mode.
 30. A method for controlling acatalytic combustion system comprising the acts of: determining one ormore temperatures associated with a catalyst in a combustor exceeding apreselected temperature value, wherein the temperature value isassociated with overheating of the catalyst; and varying at least one offuel flow and air flow to the catalyst to reduce the temperature. 31.The method of claim 30, wherein the one or more temperatures areassociated with at least one of an outlet gas temperature of thecatalyst and an outlet face temperature of the catalyst.
 32. The methodof claim 30, wherein the combustor includes at least two catalystsarranged serially and the one or more temperatures are associated withat least one of an outlet gas temperature of at least one of thecatalysts, an outlet face temperature of at least one of the catalysts,and an interstage catalyst temperature located between two seriallyadjacent catalysts.
 33. The method of claim 30, wherein varying includesdecreasing at least one of an air-to-fuel ratio and a catalyst inlettemperature.
 34. The method of claim 30, wherein the air flow is variedwith one or more of a bypass valve, bleed valve, and inlet guide vane.35. The method of claim 30, wherein at least one of the fuel flow andair flow is varied incrementally until the one or more temperatures arereduced.
 36. The method of claim 30, further including incrementallyreducing a demand value associated with one or more of the fuel flow andair flow to the system until the one or more temperatures are reducedbelow the threshold temperature.
 37. The method of claim 30, wherein theone or more temperatures are reduced by reducing fuel flow to apreburner of the system.
 38. The method of claim 30, wherein the one ormore temperatures are reduced by reducing the fuel flow to the catalyst.39. The method of claim 30, wherein the one or more temperatures arereduced by reducing catalyst inlet fuel-to-air ratio.
 40. A catalyticcombustion system, comprising: a combustor housing with a catalystdisposed therein; a first temperature probe with a field of viewdirected to an outlet face of the catalyst; one or more secondtemperature probes upstream of the catalyst and positioned to measure acatalyst inlet temperature; and one or more third temperature probesdownstream of the catalyst and positioned to measure a catalyst outlettemperature.
 41. The system of claim 40, further including at least asecond combustor housing disposed in a multi-combustor configuration.42. The system of claim 40, wherein the first temperature probe includesan ultra-violet sensor.
 43. The system of claim 40, wherein the one ormore second temperature probes are disposed within 4 inches of thecatalyst inlet face.
 44. The system of claim 40, wherein the one or moresecond temperature probes are disposed within 2 inches of the catalystinlet face.
 45. The system of claim 40, wherein the one or more thirdtemperature probes are disposed within 4 inches of the catalyst outletface.
 46. The system of claim 40, wherein the one or more thirdtemperature probes are disposed within 2 inches of the catalyst outletface.
 47. The system of claim 40, further including one or more of abypass valve, bleed valve, and inlet guide vane.
 48. A method foroperating a catalytic combustion system comprising: ramping a catalyticcombustion system having a catalyst at a first rate to a preselectedload level; and ramping at a second rate after the preselected loadlevel has been reached, wherein the second rate is less than the firstrate.
 49. The method of claim 48, wherein the preselected load level isassociated with a catalyst outlet gas temperature threshold.
 50. Themethod of claim 48, wherein the preselected load level is associatedwith a catalyst outlet face temperature threshold.
 51. The method ofclaim 48, further including pausing for a time between ramping at thefirst rate and the second rate.
 52. The method of claim 48, furtherincluding reducing operating schedules between the first rate and thesecond rate.
 53. The method of claim 48, further including reducing atleast one of a catalyst outlet gas temperature and catalyst outlet facetemperature prior to ramping at the second rate.
 54. The method of claim48, further including reducing at least one of a catalyst outlet gastemperature and catalyst outlet face temperature between ramping at thefirst rate and the second rate.
 55. A method for operating a catalyticcombustion system comprising: ramping a catalytic combustion systemhaving a catalyst at a first rate until a temperature associated withthe catalyst reaches a preselected upper value; pausing for a period oftime where the system is not ramped; and ramping the catalyst combustionsystem at a second rate subsequent to the pause.
 56. The method of claim55, wherein the period of time is such that the temperature reduces to apreselected lower value.
 57. The method of claim 55, wherein thepreselected upper value is associated with the catalyst overheating. 58.The method of claim 55, wherein the temperature includes at least one ofa catalyst outlet gas temperature and a catalyst outlet face temperature59. The method of claim 55, wherein the first rate and second rate areequal.
 60. The method of claim 55, wherein the first rate is greaterthan the second rate.